The invention relates to a slit projector comprising a light source of several light diodes arranged side-by-side and essentially in a longitudinal direction of the slit.
Such a slit projector is known from the state of the art, for example, from the Book xe2x80x9cOphthalmologic Optic Instrumentsxe2x80x9d published by Bernhard Rassow. The principle of the slit projector, as it is, for example, used in a slit lamp, is based on the fact that the refraction media of the front chamber of the eye are not highly transparent but instead a clear scattering occurs thereat in particular in the short-wave portion of the visible light. This has the result that a strongly concentrated light beam, which is sent through the optic media of the eye becomes, when viewed from the side, visible in the media similar to the beams of automotive headlights in fog. The various portions of the refraction media of the eye have a varying strong light scattering and can therefore be differentiated.
This principle of the focal illumination is perfected in the slit projector. A slitlike luminous beam of high brightness and a as high as possible color temperature (short-wave area) is used for the illumination.
A low voltage lamp has been successful in the past as the light source of such a slit projector because it enables a high light intensity with a relatively high color temperature. Halogen lamps have the advantage that they can tolerate higher stress during continuous operation and with this the color temperature increases clearly, furthermore their light is through holding only insignificantly changed. Only in a special design of a slit lamp with an extremely complicated construction there exists as the light source a Xenon high pressure lamp.
Ophthalmologists use slit projectors, with which besides the viewing of the front chamber of the eye also pictures of the transverse section or slit image of the front chamber of the eye can be taken. Good pictures of the front section of the eye require thereby a rather strong fading-out of the lens for shooting in order to achieve a good depth of sharpness. This means that the light sources must be very efficient regarding the illumination. Pictures of the front section of the eye in the optic section have up to now only been possible with an electronic flash or rather the Xenon high pressure lamp coupled into the slit illumination. In the case of the slit projector with a Xenon high pressure lamp we are dealing with a highly sophisticated and very expensive high quality device, which can be excellently utilized for complete diagnostic services and also for photography. However, this slit projector exceeds in its design and also in price by far the requirements set forth for the usual diagnostic services.
A further disadvantage when using common electronic flashes for the transverse section photography is the long charging duration of the electronic flash. Therefore, several seconds elapse always between the pictures until the electronic flash is ready again and a further picture can be taken. A total detection or scan of the front chamber of the eye by means of a photo slit lamp is therefore time consuming and expensive.
The basic purpose of the invention is therefore to provide a slit projector, which projects a slit of light to provide the necessary brightness for a viewing of the eye, and in particular also for the slit image photography, and enables a high image frequency.
This purpose is attained according to the invention in such a manner that the light source consists of several light diodes arranged essentially in a longitudinal direction of the slit, namely in the plane of the projected slit.
The inventive use of light diodes as the light source of the slit projector has several advantages. The advantage most important for the ophthalmologist is the high speed, with which the flashes needed for the slit image photography can be produced with the light diodes. Moreover light diodes are significantly compacter than the common light sources, the light diodes are more robust than the highly sensitive Xenon high pressure lamps and are noticeably less expensive.
The light diodes can then in a first embodiment according to the invention be arranged arclike or circularly lying in the plane of the projected slit. The curvature of the arc is then advantageously determined such that an as large as possible amount of light passes through the lens system.
The light diodes can in a different embodiment of the invention be arranged essentially in a plane parallel to the slit diaphragm. Main beams of the light diodes are then advantageously inclined relative to the optic axis of the lens system, and the inclination of the main beams is proportional to the distance of the light diodes from the optic axis of the lens system. The main beams of all light diodes intersect then advantageously essentially in one common point.
A slit light projection of the invention can advantageously have a second slit diaphragm in front of the lens system, whereby the slit of this second slit diaphragm is aligned with the slit of the first slit diaphragm.
The light fields can according to the invention consist of light diode chips. These light diode chips are then advantageously arranged along a straight line, whereby the connecting fields lie on both sides of the straight line. With this arrangement it is achieved that the areas of the light diode chips, which areas are uncovered by the connecting fields, lie as much as possible at the edge of the light fields reproduced on the first slit diaphragm and an as large as possible amount of light reaches the lens system.
In special embodiments it is possible for the diode lenses to be astigmatic and/or the lens system to consist of cylinder lenses. Both cases achieve a concentration of the light produced by the light fields on the slit in the first slit diaphragm.
This first slit diaphragm can according to the invention have a width of 50 to 120 xcexcm, whereas the aperture angle of the beam concentration exiting from the first slit diaphragm is less than or equal to 2.9xc2x0.
In order to obtain an advantageous scattering behavior in the eye, light diodes, which produce blue light are preferred.